1. Field of the Invention
The present invention relates to a thin semiconductor device comprising a semiconductor chip bonded to the substrate.
2. Description of Related Art
To reduce the mounting area of a semiconductor device, there is put to practical use a chip-size package serving as an IC package of which size is substantially equal to that of a semiconductor chip itself. In an example of a semiconductor device of the chip-size package type, a semiconductor chip is bonded to a substrate called an interposer. For example, a plurality of bumps are disposed at the periphery of the active surface of the semiconductor chip and bonded to the interposer substrate. For example, a plurality of soldering balls are disposed, in a grid-pattern two-dimensional arrangement, on the surface of the interposer substrate which is opposite to the surface thereof facing the semiconductor chip. Disposed inside of the interposer substrate are multi-layer wirings for wiring the bumps to the soldering balls in a two-dimensional arrangement.
Recently, to further reduce a chip-size package in thickness, it has been tried to grind the non-active surface of a semiconductor chip or to reduce a thickness of the interposer substrate. This disadvantageously reduces the rigidity of the chip-size package, causing the same to be undesirably warped at the time of storage or assembling. This involves the likelihood that when mounting such a warped chip-size package on a mounting board, all the soldering balls cannot always securely be bonded to the lands on the mounting board. More specifically, there is a possibility of elements being defectively mounted.
It is an object of the present invention to provide a semiconductor device so arranged as to prevent warp.
According to the present invention, a semiconductor device comprises: a substrate; a semiconductor chip having one surface bonded to the surface of the substrate; and a warp preventing sheet bonded to the other surface of the semiconductor chip. According to the arrangement above-mentioned, the semiconductor chip will expand and contract substantially equally at both surfaces thereof. Therefore, even though the semiconductor chip is made thin, it is possible to prevent the occurrence of undesired warp.
Preferably, the warp preventing sheet has a coefficient of elasticity substantially equal to that of the substrate. For example, the warp preventing sheet preferably has a coefficient of elasticity not less than {fraction (1/10)} of the coefficient of elasticity of the substrate and not greater than 10 times the coefficient of elasticity of the substrate. According to the arrangement above-mentioned, the semiconductor device can effectively be prevented from being warped.
Preferably, the warp preventing sheet has a coefficient of thermal expansion substantially equal to that of the substrate. For example, the warp preventing sheet preferably has a coefficient of thermal expansion not less than {fraction (1/10)} of the coefficient of thermal expansion of the substrate and not greater than 10 times the coefficient of thermal expansion of the substrate. According to the arrangement above-mentioned, the semiconductor chip will thermally expand and contract equally at both surfaces thereof. Thus, the semiconductor device can effectively be prevented from being warped.
Preferably, the base of the warp preventing sheet is made of material identical with that of the base of the substrate. According to the arrangement above-mentioned, the semiconductor chip will expand and contract equally at both surfaces thereof. This can prevent the semiconductor device from being warped.
More specifically, the base of each of the substrate and the warp preventing sheet may be a polyimide resin.
Preferably, the warp preventing sheet has a thickness substantially equal to that of the substrate. According to the arrangement above-mentioned, the semiconductor device can more securely be prevented from being warped. In particular, when the warp preventing sheet and the substrate which are made of the base having the same material, are made equal in thickness to each other, both surfaces of the semiconductor chip can be made equal in condition to each other. This securely prevents the semiconductor device from being warped.
These and other features, objects, advantages and effects of the present invention will be more fully apparent from the following detailed description set forth below when taken in conjunction with the accompanying drawings.